1. Field of the Invention
The present invention relates to a projection apparatus and a distance measurement method.
2. Description of the Related Art
Recently, a data projector has been come into wide use as a projection apparatus. The projection apparatus projects many kinds of images on a screen. The images include an image on a display of a personal computer, a video signal image and an image of an image data stored in a memory card.
In many cases, the projection apparatus uses a small high-luminance light source such as a metal halide lamp and an ultra-high pressure mercury vapor lamp. The projection apparatus irradiates light emitted from the light source to a display device called a liquid crystal device and a digital micro-mirror device (DMD) as three primary lights via color filters using a light source optical system. Further, the projection apparatus projects a transmitted light or reflected light of the display device on a screen via a projection optical system having a zoom function, that is, a lens group.
In such a projection apparatus, a projection screen is obliquely inclined with respect to a plane vertical to an optical axis of the projection light emitted from the projection apparatus. In this case, the following phenomenon occurs; specifically, a projected image is distorted like a trapezoid. In order to solve the foregoing problem, for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-39558 discloses the following technique. According to the technique, distances from several points on the projection screen to the projection apparatus are measured using a phase-difference distance measurement sensor. In this way, the relatively positional relationship of the projection apparatus and the projection screen is determined. Based on the foregoing positional relationship, the foregoing trapezoidal distortion of the projected image is corrected using image processing without physically controlling the relatively positional relationship of the projection apparatus and the projection screen.
Moreover, Jpn. Pat. Appln. KOKAI Publication No. H7-84045 discloses the following technique. According to the technique, distance measurement is made using a laser distance measurement sensor in place of the phase-difference type. The laser distance measurement sensor has the following merits compared with the phase-difference type. Namely, the distance measurement speed is fast, and distance measurement accuracy is high.
However, the following problem arises. Specifically, in the projection apparatus, a distance to the projection screen is measured using laser. In this case, when an image having the same wavelength component as laser beam is projected, distance measurement accuracy is reduced due to an influence of reflected light as the image.